Aluminum nitride and silicon nitride have recently emerged as important nonlinear optical materials in integrated photonics for their quadratic and cubic optical nonlinearity, respectively. A composite aluminum nitride and silicon nitride waveguide structure, if realized, will simultaneously allow highly efficient second- and third-harmonic generation on the same chip platform and therefore assists 2f-3f self-referenced frequency combs. On-chip third-harmonic generation, being a higher-order nonlinear optics effect, is more demanding than second-harmonic generation due to the large frequency difference between the fundamental- and third-harmonic frequencies, which implies a large change of refractive indices and more stringent requirements on phase matching. In this work we demonstrate high-efficiency third-harmonic generation in a high-Q composite aluminum nitride/silicon nitride ring cavity. By carefully engineering the microring resonator geometry of the bilayer structure to optimize the quality factor, mode volume, and modal overlap of the optical fields, we report a maximum conversion efficiency of $180\%{\mathrm{W}}^{-2}$, corresponding to an absolute conversion efficiency of 0.16%. This composite photonic chip design provides a solution for efficient frequency conversion over a large wavelength span, broadband comb generation, and self-referenced frequency combs.

中文翻译：

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氮化铝/氮化硅复合微环中的高效三次谐波产生

氮化铝和氮化硅由于其二次和三次光学非线性而最近已成为集成光子学中的重要非线性光学材料。如果实现了复合氮化铝和氮化硅波导结构，则将同时在同一芯片平台上实现高效的二次谐波和三次谐波生成，因此有助于2f-3f自参考频率梳。片上三次谐波产生是一种高阶非线性光学效应，由于二次谐波产生的基频和三次谐波之间的频率差较大，这意味着二次折射率的变化较大，因此片上三次谐波的产生比二次谐波产生的要求更高。对相位匹配的要求更加严格。在这项工作中，我们展示了高效率的三次谐波产生Q复合氮化铝/氮化硅环腔。通过仔细设计双层结构的微环谐振器几何形状以优化光场的品质因数，模式体积和模式重叠，我们报告了最大转换效率为$180％{\mathrm{w\; ^}}^{-\mathrm{2个}}$，对应的绝对转换效率为0.16％。这种复合光子芯片设计提供了一种解决方案，可在大波长范围内进行有效的频率转换，宽带梳状波产生和自参考频率梳状。